1. Field of the Invention
The invention relates in general to an evaporation system. More particularly, this invention relates to a moving evaporation device of an evaporation system.
2. Description of the Related Art
The current thin film deposition technique comprises physical vapor deposition and chemical vapor deposition. One of the very popular processes for physical vapor deposition includes evaporation. Via heating the evaporation source, thin film deposition is performed by a saturation vapor tension of the evaporation source at a high temperature in the evaporation process. The deposition of thin film includes a series of atom absorption, surface diffusion of the absorbed atom and agglomeration under proper stage or kink position.
A typical evaporation system comprises a vacuum evaporation chamber for execution vacuum evaporation and an external vacuum system to provided vacuum to the evaporation chamber. The evaporation chamber further comprises an evaporation boat and a rotatable wafer table. The evaporation boat is located at a lower portion inside of the evaporation chamber to carry an evaporation source. The material for making the evaporation boat includes high temperature material. The rotatable wafer table is located at an upper portion inside the evaporation chamber. A wafer or a substrate is fixed on the rotatable wafer table, which is rotating during thin film deposition. When a proper amount of current flows through the evaporation boat, the evaporation source is heated by the heat generated by resistance effect of the evaporation boat. When the evaporation source is heated up to near a melting point, the originally solid evaporation source has thus a very strong evaporating rate. The evaporated particles are then deposited on the wafer located over the evaporation source.
FIGS. 1A to 1D show a conventional evaporation system. In FIG. 1A, the evaporation system 100 comprises an evaporation chamber 102 and a vacuum system 104. The external vacuum system 104 is connected to the evaporation chamber 102 to provide a vacuum environment. The evaporation chamber 102 comprises an evaporation boat 106 and a rotatable wafer table 108. The rotatable wafer table 108 is located at an upper portion inside the evaporation chamber 102 to fix a wafer 110 thereon. To improve the uniformity for thin film deposition, the rotatable wafer table 108 is rotating during deposition. The evaporation boat 106 under the rotatable wafer table 108 is located at a lower portion inside the evaporation chamber 102 to carry an evaporation source 112. When a current flows through the evaporation boat 106, a heat is generated via resistance effect. The solid evaporation source 112 is then heated until reaching a melting point at which the evaporation rate is high. The particles of the evaporation source 112 are then evaporated and deposited on the wafer 110.
FIG. 1B shows a cross sectional view of the evaporation boat as illustrated in FIG. 1A. The evaporation boat 106 is a crucible having a central recess 114 at which the evaporation source 112 is located. The heat generated via resistance effect evaporates the evaporation source 112 for deposition.
FIG. 1C is the cross sectional view of the wafer 110 after being deposited with a thin film, and FIG. 1D shows the evaporation range. In FIG. 1C, after the evaporation process, the wafer 110 comprises a thin film 116 thereon. As mentioned above, to improve the uniformity, the wafer table 108 is rotating during deposition. However, as shown in FIG. 1D, a non-uniform distribution of the thin film 116 still occurs.
Referring to FIG. 1D, the deposition coverage can be partitioned into two regions 118 and 120. During thin film deposition, particles of the evaporated source 112 reach to a central region 118 first, and then diffuse outwardly to the region 120. As a result, more particles are deposited in the central region 118. The deposited particles becomes more and more diluted as the particles diffuse outwardly. The non-uniformity does not only affect the precision of the subsequent process, but also may cause the damage of the wafer.
The invention provides a movable evaporation device to improve the uniformity of a thin film deposited by evaporation process, so as to reach the requirements for precision and device dimension. The moving rate of the evaporation source is controlled by the evaporation device so as to obtain a uniform thin film. In addition, the distance between the evaporation source and the wafer is adjusted to control the deposition rate.
The movable evaporation device is applied in an evaporation system that comprises an evaporation chamber and a vacuum system. The movable evaporation device is located at a lower portion inside the evaporation chamber, and the vacuum system is external and connected to the evaporation chamber to provide a vacuum environment inside the evaporation chamber. The evaporation chamber further comprises a rotatable wafer table at an upper portion of the evaporation chamber to carry a wafer. The movable evaporation device comprises more than one movable evaporation boat to carry evaporation source. Each movable wafer boat further comprises a wafer boat and a moving arm. The moving arm is connected to a bottom of the evaporation chamber and can make a rotation for 360xc2x0. The length of the moving arm is determined by the number and position of the wafer boats.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.